Abstract

Electrical stimulation is used for example to treat neuronal disorders and depression with deep brain stimulation or transcranial electrical stimulation. Depending on the application, different electrodes are used and thus different electrical characteristics exist, which have to be handled by the stimulator. Without a measuring device the user would have to rely on the stimulator being able to deliver the needed stimulation signal. Therefore, the objective of this paper is to present a method to increase the level of confidence with characterization and modelling of the electrical behavior by using the example of one channel of our stimulation device for experimental use. In several simulation studies with an electrode model with values in a typical range for cortical applications the influence of the load onto the stimulator and the possibility to pre-estimate measuring signals in complex networks are shown.

A) Example of a simulation work frame for two stimulation channels including stimulator models (first block), an electrode tissue network with 4 electrodes (third block) and isolated measuring channels (second block) with averaging capabilities including current measuring resistors which are in series with the stimulator’s positive output and the load.B) Three electrode models with different complexity a) with a constant phase element (ZCPE), Warburg impedance (ZW), series resistor (RS) and faradaic resistor (RF), b) like a) but without Warburg impedance, c) simple electrode model: constant phase element is repleaced by the double layer capacitance (CD)

(A) comparison of the calculated error after data approximation with a second order and a third order polynomial for different stimulation amplitudes; (B) comparison of the error between the preset stimulation current and the measured stimulation current (amplitudes) before and after adjustment. The almost periodic trend correlates with the used measurement ranges of the measuring device; (C) representation of the normalized stimulation current amplitude for different load resistors; (D) representation of the calculated output impedance of the stimulator for various load resistors

(A) correlation between the model element values (CD: double layer capacitance; RS: series resistor; RF: faradaic resistor; var: index for changing value) and the normed stimulation amplitude; (B) and (C) correlation between the model element values and the slew rate of the stimulation signal; (D) influence of the faradaic resistor of large pulse length; (E) comparison of a real measurement (left) and the result of a simulation for an electrode model with CD = 120 nF and RS = 1.5 kΩ. Stimulation signal: biphasic pulse with amplitude of ±30 μA, pulse time of 500 μs and 10 ms periode time. In both cases the signals were measured with 5 kΩ resistor in series to the load.